1. Field of the Invention
This invention generally relates to data processing, and more specifically relates to allocation of shared resources in a computer system.
2. Background Art
Since the dawn of the computer age, computer systems have evolved into extremely sophisticated devices that may be found in many different settings. Computer systems typically include a combination of hardware (e.g., semiconductors, circuit boards, etc.) and software (e.g., computer programs). As advances in semiconductor processing and computer architecture push the performance of the computer hardware higher, more sophisticated computer software has evolved to take advantage of the higher performance of the hardware, resulting in computer systems today that are much more powerful than just a few years ago.
The combination of hardware and software on a particular computer system defines a computing environment. Different hardware platforms and different operating systems thus provide different computing environments. In recent years, engineers have recognized that it is possible to provide different computing environments on the same physical computer system by logically partitioning the computer system resources to different computing environments. The iSeries computer system developed by IBM is an example of a computer system that supports logical partitioning. If logical partitioning on an iSeries computer system is desired, resource and partition manager code (referred to as a “hypervisor” in iSeries terminology) is installed that allows defining different computing environments on the same platform. Once the resource and partition manager is installed, logical partitions may be created that define different computing environments. The resource and partition manager manages the logical partitions to assure that they can share needed resources in the computer system while maintaining the separate computing environments defined by the logical partitions.
A computer system that includes multiple logical partitions typically shares resources between the logical partitions. For example, a computer system with two logical partitions could be defined that allocates 50% of the CPU to each partition, that allocates 33% of the memory to the first partition and 67% of the memory to the second partition, and that allocates two different I/O slots to the two logical partitions, one per partition. Once logical partitions are defined and shared resources are allocated to the logical partitions, each logical partition acts as a separate computer system. Thus, in the example above that has a single computer system with two logical partitions, the two logical partitions will appear for all practical purposes to be two separate and distinct computer systems.
One problem with known logically partitioned computer systems occurs when hardware resources need to be transferred between logical partitions. For example, if a PCI slot in a first logical partition needs to be transferred to a second logical partition, the PCI slot must first be removed from the first logical partition, and the PCI slot can then be allocated to the second logical partition. Note, however, that once the PCI slot has been removed from the first logical partition, in the prior art two logical partitions might compete for control of the PCI slot at the same time. In addition, when a PCI slot is allocated to a different logical partition, it may contain data from the previous logical partition that could be compromised under certain circumstances. Furthermore, the PCI slot may be configured in a particular state suitable for the first logical partition, which is not necessarily suitable for the second logical partition. Without a way to dynamically transfer I/O resources in a logically partitioned computer system without the drawbacks known in the art, the computer industry will continue to suffer from potentially insecure and inefficient mechanisms and methods for performing I/O resource transfers in logically partitioned computer systems.